Flotation reactor and method for flotation

ABSTRACT

The invention relates to a flotation method and a flotation reactor. The invention provides a method and a device, wherein the formation of the gas bubbles needed for flotation are produced by catalytic reaction of a chemical substance, i.e. H 2 O 2 , thereby saving energy and reducing the number of compressors. Flocculation also occurs in a tangential flow in the funnel-shaped expansion ( 12 ) of an admission pipe ( 8 ) so that a flocculation basin with a stirrer is no longer required.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT/DE98/03733 filed Dec. 16,1998 and based on German application 197 56 962.5 of Dec. 20, 1997 underthe International Convention.

FIELD OF THE INVENTION

The invention relates to a flotation reactor and a method of flotation.

BACKGROUND OF THE INVENTION

According to the state of the art, various flotation processes areknown. Thus in the publication “Umweltschutz Entsorgungstechnik” ofProf. Dr. P. Kunz 2. Auflage 1990 Vogel Book Publishing Co. under theheading “Treatment of Waste Water” on pages 85-86, electroflotation andpressure-expansion flotation are disclosed.

These processes are also known from the work “Wassertechnologie—Fallung,Flockung, Separation” of Hermann H. Hahn of Springer-Verlag Berlin,Heidelberg 1987.

In pressure-expansion flotation, water under pressure is charged withgas and conducted into a flotation chamber. Upon pressure relief, thereis an expansion of the gas in the liquid, the gas bubbles out andflotates the solids to be separated from the liquid which can berecovered from the surface of the liquid.

In electroflotation, a gas rising in the liquid is generated byelectrolysis and flotates the solids to be separated.

Both processes are used in an industrial scale, but have significantdrawbacks. Thus expansion flotation requires an expensive andpressurizable apparatus.

As a result of the rapid pressure expansion, the gas formation is rapid,as a result of which turbulence arises which can again break up theflocculate.

In both processes, the flocculating step must precede the flotation stepin which the solids precipitate out in a flocculation basin and whereinthe solids agglomerate to larger flocculates.

Electroflotation gives rise to high operating costs because of the highcurrent requirements. Both processes have a high energy consumption.

OBJECT OF THE INVENTION

It is therefore the object of the invention to provide a process and anapparatus which is characterized by a substantially-reduced energyconsumption and can avoid the need for expensive and dear apparatus andin which a breakup of the flocculate by turbulence is suppressed.

SUMMARY OF THE INVENTION

The object is achieved with a flotation reactor with a flotation space,an inlet for the flotation liquid and a gas source, characterized inthat the gas source is a catalyst which is brought into contact with asubstance which is converted to a gas thereby.

With the method and the apparatus according to the invention it ispossible directly to carry out flotation of solids in anenergy-conserving manner at low apparatus cost. The danger thatflocculates will be destroyed by the flotation is very low. Theflotation is effected with very small gas bubbles and is highly uniformand of low turbulence.

The flotation reactor can have its flotation space coated with thecatalyst. The catalyst can have at least one of its components selectedfrom the group of manganese dioxide and active carbon. The flotationreactor can have means at its bottom region for introducing a substancewhich is converted on the catalyst to the gas. The flotation reactor canalso have in the bottom region means for introducing the flotationliquid.

The means for introducing the water for flotation can be adownwardly-directed pipe which at its lower end or in its lower third,has outlet openings and which widens upwardly in the form of a funnel.At the funnel, means can be provided for tangentially admitting theflotating liquid. The flotation reactor can have a downwardly-directedtube and a funnel-shaped converging narrowing. The pipe beneath theoutlet openings can have a bottom. The funnel-shaped narrowing can be soconfigured that it extends above the pipe cross section so that norising floc or gas bubbles can enter the outlet opening.

The walls of the flotation space can widen upwardly in the form of afunnel.

The aforementioned flotation chamber can be located in a furthersurrounding flotation chamber and the walls of the flotation chamber canbe coated with a catalyst which catalyzes a chemical reaction from whicha gas is produced.

In this embodiment the flotation space in its lower region has means forintroducing a substance which forms a gas by the chemical reaction. Theflotation space can be so constructed that it surrounds thefirst-mentioned flotation space with its wall radially symmetricallywhereby it forms below the means for introducing a substance producing agas by the chemical reaction, a closed vessel which runs to a centralincline and whereby the wall of the flotation space leaves free anintermediate space with the wall of the flotation reactor outside thefunnel means can be provided for concentration of gas bubbles in theflotation space. This means for concentrating the gas bubbles can be aconical ring.

The second flotation space can be provided at its bottom in the form ofan incline for the discharge of the flotated liquid which can beeffected through a U-shaped pipe. The U-shaped pipe can be telescopinglyelongatable.

The flotation reactor can have means for separating the flotate.

The flotation method is characterized in that a chemical reaction iscarried out for producing gas bubbles. The chemical reaction can be acatalytic reaction, for example, a decomposition of hydrogen peroxide towater and oxygen. As the catalyst, manganese dioxide and/or activecarbon can be used.

The substance which decomposes to the gas in the chemical reaction canbe admitted to the lower region of a flotation space. The substance tobe flotated can be supplied in a tangential flow and can then flow in adownwardly-directed stream.

The liquid quantity leaving the flotation reaction is preferably matchedto the flotation liquid at the inlet to the flotation reactor.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE of the drawing shows an apparatus according to theinvention in a schematic form.

SPECIFIC DESCRIPTION

In the drawing a flotation reactor 1 is illustrated which has a firstflotation space 2 whose walls 3 and bottom 4 are coated on theirinwardly-directed sides with a catalyst 5. The flotation space 2 iswidened upwardly in the form of a funnel 6 and, provided at its lowerend with an inlet 7 for the solids to be flotated in a liquid. In theflotation space 2, as a means for introducing the solids to be flotated,there is a vertically downwardly directed pipe 8 which at its lower endis formed with a bottom 9 and is closed with a funnel-shaped narrowing 9a. In the lower region of the tube 8 there are outlet openings 10 forthe material to be flotated. The funnel-shaped narrowing 9 a forms meansfor conducting and guiding a flowing liquid in the form of a flange 11.

The pipe 8 widens at its upper end also in the form of a funnel 12 andhas a further inlet 13 for the solids to be flotated in a liquid.

The flotation space 2 comprises a supply conduit 14 for H₂O₂ which opensat the bottom. The first flotation space 2 is located in a secondflotation space 15 which is comprised of a conical ring 16 serving as ameans for concentrating the gas bubbles. The second flotation space 15is defined substantially by the wall 3 of the first flotation space 2,the upper region of the reactor wall 17, the conical ring 16, the funnel6 and, in its lower region, by the first flotation space and is boundedby the upwardly open wall 18 which is closed by the bottom 4 a and runsdownwardly inwardly toward the center via an inclined wall 19.

The inclined wall 19, together with the bottom 4 a of the firstflotation space closes a chamber 20 which is provided with openings 21traversed by a substance which liberates a gas by chemical reaction andthe supply pipe 22 for this substance. The second flotation space 15 isalso coated internally with the catalyst 5. The coatings cover theoutwardly-directed side of the wall 3 of the flotation space 2 as wellas the inwardly-turned side of the wall 18 and the incline 19. Theconical ring 16 as well as regions of the reactor wall 17 can also becoated with catalyst.

The flotation reactor 1 runs conically below the incline 19, in itsturn, into an incline 23 which surrounds the supply ducts 14 and 22. Thespace 17 enclosed by the incline 23 extends outside the flotationreactor 1 in the form of a telescopingly elongatable U tube 25. Betweenthe wall 17 and the funnel 12 a rotating reamer of flotated solids 26 isprovided.

In operation, the water charged with the solids to be flotated, togetherwith a flocculating agent, is fed via the inlet 13 into the funnel 12 ina tangential flow. By the introduction of this suspension in the form ofa tangential flow, flocculation is so optimized that the provision of aflocculating basin upstream of the reactor can be avoided since theflocculent can ripen during the circular movement. The solids to beflotated agglomerate during the circular movement in the funnel 12especially well to lodge downwardly sinking flotatable flock.

In the funnel, the water with the flotatable solid passes downwardlythrough the pipe 8. The water emerges from the pipe 8 at the outletopenings 10 and thus flows into the first flotation space 2 which iscoated with a catalyst 5.

As the catalyst 5, active carbon 4 magnesium dioxide can be used. H₂O₂is fed through the supply line 14, preferably at the lowest point in theflotation space 2. The H₂O₂ decomposes on the catalyst surfaces of thecatalyst coated walls 3, pipe 8 and bottom 4 to water and oxygen. As aresult of this decomposition, extremely fine gas bubbles are formedwhich calmly and with low turbulence move upwardly in the flow of water.This calm movement of the gas bubbles is responsible for the transportof the flocculated solids, without breaking them up, and especiallyeffective flotation.

With the upwardly-directed flow of the flotation water, the flotationpath travels along the narrowing 9 a as well as along the flange 11. Asa result, the reentry of flocculated solids and gas bubbles in theinlets 10 is prevented.

The bottom 9 provided at the lower region of the pipe 8 prevents thefloc from settling in the narrowing 9 a and fouling the latter. Thewater involved in the process passes upwardly out of the first flotationspace 2 along its path through the funnel-shaped opening. At thislocation, the rotation reamer can separate the solids of the flocculatedsolid materials. Already at this stage, the flotation results are verygood.

For the case in which some of the floc below the funnel 6 settles, thereis effected a further introduction of H₂O₂ into the second flotationspace. In this space the further H₂O₂ comes into contact with the walls18 and incline 19 which are coated with catalyst, the further H₂O₂ beingadmitted through the openings 21 in the lower region of the secondflotation space. The resulting rising oxygen flotates the floc in thesame way as in the first flotation space from the liquid directeddownwardly and passing between the reactor wall 17 and wall 18. Sincethe lower region of the second flotation space 15 between the wall 18and the first flotation space 2 represents an especially calm zone, theH₂O₂ is not diluted by flow and the flotation is especially effective.

To amplify the flotation effect, there is found in the upper region ofthe second flotation space 15, a conical ring 16 which effects aconstriction of the flow cross section and thus a concentration ordensification of the upwardly flowing oxygen bubbles. An additionalconcentration of the oxygen bubbles arises through the accumulation ofthe gas bubbles from the first and second flotation spaces 2 and 15 atthe location at which the funnel 12 ends. From there, the flotationsludge passes to the liquid surface and can be removed. The excellentflotation results of the method of the invention is especiallysignificant since it enables a good and plentiful attachment of gasbubbles to the particles or bloc. The conical ring 16, in an especiallypreferred embodiment of the invention is height adjustable so that as aresult, a further reduction or spread of the flowthrough cross sectionis possible between the funnel 6 and the conical ring 16.

The water freed from solids flows downwardly through the space 24 andthe U tube 25 from the flotation reactor 1. Because of the configurationof the incline 23 at the outlet region, the liquid subjected toflotation prevents the settling of particles in space 24 so that evenwith very long operation durations, there is no plugging. The U tube 25is telescopingly elongatable upwardly. As a result, an increased liquidlevel in the pipe 8 or the funnel 12 can be compensated when the liquidquantity traversing the flotation reactor must be increased for examplebecause of an increased purification requirement per unit time. Thewater level in flotation reactor 1 can thus be optimally adjusted forseparation of the flotation sludge at different water throughputs.

In the flotation of solids which have a tendency to rise in the liquid,a charging of the first flotation space 2 with the liquid to be flotatedthrough inlet 7 is possible. In this case, the flotation can be carriedout in a flocculation basin provided ahead of the apparatus but notshown in the drawing.

The method of the invention and the apparatus operates especiallyeconomically. Thus with an H₂O₂ concentration of 0.06% over a durationof 24 hours, oxygen is continuously released. The operation of thesecond flotation space 15, arranged below the first flotations space, isflocculated and depends upon the degree of charging of the apparatus ofthe invention with flocculent.

If the process is carried out with a catalytic reaction which producesoxygen as the gas, according to a feature of the invention process, anadditional enrichment of for example denitrification water from aclarifier stage of a sewage treatment apparatus with oxygen is theresult. However, it is also possible to use another chemical reactionwhich generates other flotation gases. Thus a catalytic reaction can beused in which, for example, nitrogen is formed and which can utilize adecomposition of sodium carbonate on manganese dioxide with theformation of CO₂ for flotation.

In the fabrication of the flotation reactor 1 according to the inventionthe catalyst can be applied by conventional adhesive to the walls inthat catalyst powder can be spread onto walls to which an adhesive isapplied and before the adhesive hardens. It will be self-understood thatfinished catalyst plates can also be applied in the reactor.

The supply of a flocculating agent is flocculative and depends upon theconditions present at the time. As a rule, polyaluminumchloride (PAC) orFeCl₃ is used as the flocculating agent. The supply of the liquid to beflotated through the inlet 7 of pipe 8 is so effected that theflocculate sludge does not accumulate at the center of the flotationspace 2, thereby improving the space utilization.

The substance needed for the catalytic production of gas, like H₂O₂, ispreferably supplied at the lowest point in the flotation spaces 2 and 15since, in this case, the stretch available for flotation is a maximum.The openings 10 and 21 can however also be provided at locations spacedabove the bottom. A foreshortening of the pipe 8 and a relatedpositioning of outlet openings 10 for the flotating liquid upwardly,gives rise to the formation of a quiescent zone in the lower entryregion for H₂O₂ so that at this location scarcely any dilution of theH₂O₂ occurs.

The catalyst coated elements in the form of pipes or plates can also bebuilt into previously made flotation reactors. They can, depending uponthe application, replace the process technology expensive pressureexpansion or electroflotation in a cost-effective manner or can be usedto complement existing apparatus. The range of applications includes forexample the treatment of drinking and waste water in municipalities aswell as water treatment in the industrial field. Furthermore, the methodand the apparatus of the invention can be used as a preliminary stagefor reducing the load on filters.

What is claimed is:
 1. A flotation reactor comprising: a flotationreactor housing having respective walls; inner and outer walls in saidreactor defining between them a narrow upwardly extending flotationspace opening into a wider outlet for flotated solids; at least oneinlet for a flotation liquid and for flotatable solids communicatingwith said flotation space at a lower portion thereof whereby theflotation liquid and flotatable solids rise between said inner and outerwalls in said space; means for introducing into said reactor housing areactive liquid which flows along said walls and is catalyticallyactivatable to liberate a flotation-promoting gas to effect flotation ofsaid solids in said flotation liquid whereby flotated solids are formed;and a catalyst fixed to and coating at least some of said walls andcapable of activating said reactive liquid to produce saidflotation-promoting gas.
 2. The flotation reactor defined in claim 1,wherein said catalyst is selected from the group which consists ofactivated carbon and manganese dioxide.
 3. The flotation reactor definedin claim 2 wherein said inner and outer walls are concentric cylindersand said means for introducing said reactive liquid includes a pipeopening upwardly in said housing at a bottom thereof generally centrallybelow said cylinders.
 4. The flotation reactor defined in claim 3wherein said at least one inlet includes a downwardly extending ductopening generally centrally at a lower portion of said housing with aplurality of openings in a lower third of said duct and widening at anupper end into a funnel.
 5. The flotation reactor defined in claim 4,further comprising a supply line communicating tangentially with saidfunnel for supplying said flotation liquid and said solids thereto. 6.The flotation reactor defined in claim 4 wherein said duct has a lowerend formed with a downward conical convergence below said openings. 7.The flotation reactor defined in claim 6 wherein said duct has a bottombelow said openings and above said downward conical convergence.
 8. Theflotation reactor defined in claim 6 wherein said conical convergenceextends outwardly beyond said openings to prevent rising gas bubbles andflocculate from entering said openings.
 9. The flotation reactor definedin claim 3 wherein said outer wall is provide with a funnel at an upperend thereof forming said wider outlet.
 10. The flotation reactor definedin claim 9 wherein said funnel opens into another flotation chamber insaid housing surrounding said outer wall.
 11. The flotation reactordefined in claim 10 wherein said other flotation chamber is definedbetween walls coated with a gas-generating catalyst.
 12. The flotationreactor defined in claim 11 wherein said means for introducing saidreactive liquid includes a pipe opening into said other flotationchamber at a bottom thereof.
 13. The flotation reactor defined in claim12 wherein said other flotation chamber is formed with a wall coaxiallysurrounding said outer wall and spaced inwardly from a wall of saidhousing, and having a downwardly converging conical bottom.
 14. Theflotation reactor defined in claim 13, further comprising a concentratorfor gas bubbles between said outer wall and said housing and below saidfunnel.
 15. The flotation reactor defined in claim 14 wherein saidconcentrator is a conical ring.
 16. The flotation reactor defined inclaim 13, further comprising a conical bottom for said other flotationchamber for discharging a flotated product.
 17. The flotation reactordefined in claim 16, further comprising a U-tube for discharging saidflotated product from said conical bottom.
 18. The flotation reactordefined in claim 17 wherein said U-tube is telescopingly elongatable.19. The flotation reactor defined in claim 16, further comprising meansfor separating the flotated product.